1. Field of the Invention
The present invention relates to a recording apparatus and, more particularly, to an apparatus for recording information such as letters and characters by means of a light beam.
2. Description of the Related Art
Recording apparatus have been known which are capable of recording letters and other information on a recording medium by means of a light beam. An example of such apparatus is laser computer output microfilmer which is capable of scanning a recording material such as a microfilm with a laser beam in accordance with, for example, information output from a computer, so as to directly record the information in the form of, for example, letters on the recording material. Such a laser computer output microfilmer is disclosed, for example, in U.S. Pat. No. 4,293,202. This apparatus has an argon laser capable of emitting a laser beam, a photo-modulator for effecting photo-modulation of the laser beam in accordance with the letter information, a rotary polygon mirror for deflecting the modulated laser beam in the direction of the main scan, and a galvanometer having a deflection mirror for deflecting the light reflected by the polygon mirror in the direction of sub-scan. The rotary polygon mirror and the galvanometer in cooperation deflects the laser beam from the photomodulator both in the directions of main scan and sub-scan so that the light beam scans the recording material through a scanning lens thereby recording information in the form of, for example, letters on the recording material. The polygon mirror is driven by a motor so as to rotate at a constant speed. It is often experienced that the mirror surface of the polygon mirror is tilted or oscillated due to, for example, inclination of the shaft of the motor, with the result that the scanning beam oscillates in the direction of the sub-scan to cause a fluctuation in the recording density in the direction of the sub-scan. The described known apparatus is therefore required to be equipped with a correcting optical system for eliminating the unevenness of the recording density in the direction of the main scan. The galvanometer is adapted to control the rotation angle of the deflection mirror in accordance with synchronizing signal which is formed upon detection of a reference light beam which is first applied along the same path as the laser beam and then shunted therefrom.
The laser computer output microfilmer mentioned before, as an example of the recording apparatus which makes use of a light beam, essentially requires a correction optical system because of the use of the rotary polygonal mirror, and is required to have helium-neon laser in order to generate the reference light beam, with the result that the production cost is raised.
It would be possible to use a resonance reflection mirror known as "resonant scanner" in place of the rotary polygonal mirror so as to overcome the above-described problems, thus eliminating necessity for the correction optical system. Since the resonance deflection mirror resonates by a sine-wave oscillation, the speed of oscillation is high in the region near the maximum oscillation angle than in the region near the minimum oscillation angle, so that the scanning speed varies oscillatingly. Therefore, when the recording is effected by means of dots, the pitch of the dots is regularly changed to cause a distortion of the recorded information. The distortion of the dot image is serious particularly when information in the form of letters is recorded on the microfilm by dots because in such a case a specifically high degree of resolution on the order of, for example, 3360 dots/7.2 mm is required.